1. Field of the Invention
The invention relates to gaming apparatus and more particularly to the class of gaming apparatus known as slot machines wherein wheels having indicia on the periphery are set into rotation at the beginning of the game and which stop at locations indicating a winning or losing combination of the indicia. Gaming apparatus of this type are not limited to spinning reels as an indicator, however, since a video monitor or other display device may be employed to indicate outcome of a game to a player.
2. Background Art
The original slot machines employed mechanically controlled reels set into motion by a player actuating a mechanical arm or lever. The reels were stopped by an indexing wheel having a plurality of grooves into which were thrust a pin which was driven by a random mechanical actuator. Pay out for a winning game was made upon the basis of the depth of the groove on the reel into which the pin had entered when the reel was stopped. Ensuing developments in the art employed electrical stopping means and electronic methods of determining the angular position the reels when stopped. The most recent of reel machines use a stepper motor to drive each reel into rotation and to stop each reel at a predetermined position to indicate the outcome of the game to the player.
In the original mechanically actuated gaming apparatus the starting and stopping of the reel rotation was assumed to be substantially in a random fashion in accordance with the driving of the mechanical actuator by the player. The pay out after the reels were stopped was in accordance with the angular position of the physical reel in relation to a payline which is a fixed point indicated to the player in by means of a line or other means fixed in relation to the reels. Some apparatus incorporated multiple paylines the number of which was selected in accordance with the amount of the wager according to a pay schedule prior to initiating the game. Multiple payline apparatus are generally known as "multi-line games". The pay out odds and the amount paid out was controlled by means of the number of symbols on the physical reel and the combinations indicated to the player on an award schedule. In order to allow the operator of the game to realize a profit upon its operation, the amount returned to players by the apparatus over a large number of plays must be a percentage less than 100% of the total amount wagered over the large number of games played. The lowest probability of a win is a function of the number of reels (n) and the number of allowed stop positions on each reel (S) which is equal to S.sup.n. The parameters which may be adjusted to allow profitability with pay are the number of reels, the number of stop positions, the definition of a winning combination and the amount paid upon a winning combination. All of these must be in a proper proportion and small enough number as to not confuse the player and provide him with playing enjoyment in order to induce him to play the game. A configuration in which there are more than four reels or more physical symbol positions (stops) on the reel than 24 have been proven to be detrimental to attracting and holding the attention of a player. If the chance to hit the largest pay shown on the award schedule is the same with each game played and only one combination of symbols shown on the reels results in award of this pay, the chance that this will occur in a 4 reel 24 stop machine is 1 time in 331,776 games. This results in a severe restriction on the amount of the largest pay which can be offered by the operator and still allow his operation to remain profitable.
In later developments, Telnaes U.S. Pat. No. 4,448,419 describes a gaming apparatus in which there are a greater number of "virtual" stop positions in computer memory than physical stop positions on the physical reel. There is an actual physical symbol on each reel corresponding to each virtual position in memory, but there are a greater number of virtual positions in memory than there are physical stops on the reel. A random number generator is used to select a number corresponding to a virtual position for each reel. Since there are more virtual positions in memory than physical stops on the reel, the probability of not selecting a winning symbol within a rotation of the reels for a particular game can be increased greatly over that of the game whose outcome depended only upon physical stops. Using the same four reel game as described in the previous paragraph, but with a 72 position virtual reel gives a one in 26,873,856 chance of hitting the largest pay shown under the same conditions. This apparatus also allows the odds to be changed by varying the number of virtual stop positions in memory without physically changing the reels and symbols upon the reels. Since the outcome of a game depends entirely upon the combinations allowed by the virtual stop positions in memory, there is a certain finite step amount in adjustment of the win probability and thus a relatively laborious calculation results in predicting the odds allowed by a game developed using this method.
In a subsequent development, Mathis/Michaelson U.S. Pat. No. 5,380,008 describe an apparatus in which two random numbers are generated, the first to determine if the game is a winner or a loser and the second to determine the amount of pay to return to a player if the game is a winner. Hit frequency is defined as the probability of any win occurring in a game or percentage of winning games of total games played.
In many of the modern gaming apparatus, there is the ability to generate a random pay amount generally known as a "mystery pay". This increases player enjoyment by paying a random amount of coins at a randomly determined point distributed over a number of games. The player is not generally provided with a way of predicting when the mystery pay will occur and may lose interest in waiting for a mystery pay.